Process of depolarizing an electrolytic cell



United States Patent 3,368,927 PROCESS OF DEPOLARIZING AN ELECTROLYTIC CELL Charles H. Worsham, Fanwood, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Jan. 11, 1963, Ser. No. 250,764 2 Claims. (Cl. 136-160) This invention relates to a method of operating an electrolytic cell, particularly a low temperature cell in a manner as to maintain efliciency during continuous operation. More particularly this invention relates to a method of flushing the electrodes of a cell during operation with an acid electrolyte in order to maintain the efliciency over a prolonged period of operation.

A problem which arises during the prolonged operation of a low temperature electrolytic cell utilizing an aqueous acid electrolyte is the gradual loss of power. Such loss of power is associated with an increase in the polarization of the anode. This loss of power caused by increase in polarization of the anode has heretofore required the dismantling of the cell to reactivate or replace the electrode.

It has now been discovered that the increased polarization can be reduced to substantially the polarization of the electrode at the beginning of operation, without interruption of the operation of the cell. According to this discovery, the activity of the cell can be restored to normal by flushing the anode with the electrolyte-fuel mixture. This is accomplished by pumping the mixture of electrolyte and fuel through the cell at a rate so that the exit fuel concentration is sufficiently high to prevent severe polarization. The actual quantity of electrolyte-fuel mixture passing through the cell per unit time will be dependent on the initial fuel concentration, and current density. The exit fuel concentration is dependent upon the current density. This process involves the loss of some fuel, but has the advantage of allowing the cell to produce power continuously.

The rate at which the electrolyte-fuel mixture is passed through the cell and the time necessary for the treatment will vary according to the concentration of the fuel entering the cell and the current density at which the cell is operated. The flow rate may vary from 10 to 700 ml./hr./0.1 ft. however, normally the flow rate will vary from 200 to 550 ml./hr./0.1 ft. for a period of about 1 to 3 hours.

Typical minimum rates are set forth in Table I below. Such minimums, if reduced, result in increased polarization. Methanol was used as the fuel to obtain the following data.

When the minimum rate of flow is reduced, increased polarization results. However, excess flow, i.e. rate above 700 ml./hr., does not further reduce the polarization.

3,368,927 Patented Feb. 13, 1968 ice This result is shown in Table 11 below. Methanol was used as the fuel.

TABLE II 5 Vol. Percent Fuel Current Density, Polarization Flow Rate, In Out amps/it. Volts m1./hr./0.1 It? Table II shows that when the volume of fuel coming out of the cell falls below 0.32 vol. percent at 50 amps./ ft. or 0.52 vol. percent at 100 amps./ft. the polarization increases sharply. However, no appreciable effect is caused by an increase in the vol. percent of fuel leaving the cell.

During the flushing operation, the polarization will remain substantially steady at the increased level during most of the period and then will rapidly drop to normal polarization. When the polarization returns to normal the flow rate can be returned to that rate at which the highest efiiciency of fuel conversion is obtained.

For the purposes of this invention, a low temperature fuel cell, and as recognized by the art, is a fuel cell which operates below 500 C.

The process of the invention is applicable to low temperature fuel cells employing aqueous acid electrolytes and liquid hydrocarbons and oxygenated hydrocarbon fuels. The electrolytes of this invention include sulfuric and phosphoric acids in concentrations of from about 10 to 55 wt. percent. The following are submitted as examples of fuels that are operable in the invention. Fuels such as unsaturated hydrocarbons such as butane-1, ethylene, acetylene, propylene; hydrocarbons such as propane, bu-

tane, ethane; alcohols such as methanol, ethanol, ethylene glycol, propanol, butanol; carbonyl hydrocarbons such as formaldehyde, acetone and organic acids such as acetic and propionic acids. The foregoing list is illustrative only and is not exhaustive of the liquid organic compounds that may be utilized as fuels when the invention is operable.

The method of the invention is operable at any temperature above the freezing point and below the boiling point of the aqueous acid electrolyte. Preferably the flushing is conducted at a temperature between room temperature and the cells operating temperature; i.e., 25 to 110 C. Most preferably the flushing is conducted at a temperature between 75 and 100 C.

The following examples are presented for purposes of illustration only and the details therein should not be construed as limitations upon the true scope of the invention as set forth in the claims.

Example 1 Example 2 A- fuel cell was operated for 1029 hours at 82 C. and 50 amps/ft. utilizing an anode comprising an 80 mesh of 0.1 ft. platinum screen with a Pt-black catalyst employing a 30 wt. percent sulfuric acid electrolyte and an average fuel concentration of about 1.9 vol percent. At the end of the 1029 hour run, the polarization had increased from 0.58 to 0.61 volt. The electrolyte-fuel mixture was pumped through the cell at a rate of about 500 ml./hr. for 3 hours. The polarization was reduced to 0.59 volt.

What is claimed is:

1. A method of reducing the polarization of an electrode which has been increased during use in a low temperature electrolytic cell employing an aqueous acid electrolyte with methanol mixed therewith, without interruption of the operation of the cell which comprises passing the aqueous acid electrolyte-methanol mixture through the cell at a rate of about 200 to 550 ml./hr./0.1 ft. until the increased polarization drops to the normal operating polarization.

2. A method of reducing the polarization of an electrode which has been increased during use in a low temperature electrolytic cell employing an aqueous acid electrolyte and an organic liquid fuel admixed therewith, without interruption of the operation of the cell which comprises passing the liquid fuel-aqueous acid electrolyte mixture through the cell at a rate of about 200 to 550 ml./hr./0.1 ft. for a period of time of from about 1 to about 3 hours.

References Cited UNITED STATES PATENTS 2,384,463 9/1945 Gunn et al. 136-86 2,925,454 2/1960 Justi et al. 136-86 735,971 8/1903 Halsey 136160 2,921,111 1/1960 Crowley et a]. 136-l60 ALLEN B. CURTIS, Primary Examiner.

W'INSTON A. DOUGLAS, JOHN H. MACK,

Examiners.

D. L. WALTON, Assistant Examiner. 

1. A METHOD OF REDUCING THE POLARIZATION OF AN ELECTRODE WHICH HAS BEEN INCREASED DURING USE IN A LOW TEMPERATURE ELECTROLYTIC CELL EMPLOYING AN AQUEOUS ACID ELECTROLYTE WITH METHOANOL MIXED THEREWITH, WITHOUT INTERRUPTION OF THE OPERATION OF THE CELL WHICH COMPRISES PASSING THE AQUEOUS ACID ELECTROLYTE-METHOANOL MIXTURE THROUGH THE CELL AT A RATE OF ABOUT 200 TO 559 ML./HR./0.1 FT.2 UNTIL THE INCREASED POLARIZATION DROPS TO THE NORMAL OPERATING POLARIZATION. 